1. Field of the Invention
The present invention relates generally to monitoring equipment and more specifically relates to equipment for monitoring physiological parameters.
2. Description of the Prior Art
The monitoring of various physiological parameters is fairly common in the art. A typical example of a monitoring system may be seen in U.S. Pat. No. 3,799,147 issued to Adolph et al. This reference teaches a system for diagnosing myocardial infarction based upon the frequency response of EKG and acoustic signals. It is interesting to note that the techniques and apparatus used by Adolph et al are typical of what is currently in use in that the primary processing circuits operate in the time domain in analog fashion. A primary disadvantage of such a monitoring technique is that the signals to be monitored must be processed and monitored in real time--that is to say, must retain their relationship in the time domain. The effect of this is to increase the required bandpass of the equipment used and any communication link employed.
An example of a system measuring physiological parameters using digital data may be found in U.S. Pat. No. 4,214,589 issued to Sakamoto et al. This reference teaches the determination of blood pressure using measurements of pressure, Korotkov sound and other inputs. Upon examination of Sakamoto et al, however, one determines that the information that is digitized from the pressure detector is yet transmitted to the processing apparatus in relationship to the time domain. Again, as in the previous case, that requires that the bandpass of the system be sufficient to operate within real time.
Other examples of monitoring systems that employ digitized information having a relationship to real time may be found in such references as U.S. Pat. No. 4,006,737 issued to Cherry and U.S. Pat. No. 4,073,011 issued to Cherry, et al. Notice that in these references, the electrocardiographic computer disclosed speeds up real time such that EKG signals may be reviewed in much shorter time than the time required for gathering the data. In fact, a twenty-four hour tape of information may be processed in as short a time as twelve minutes. However, notice that the processing involved is yet related to real time, requiring relatively wide bandpasses to permit the handling of the information in true relationship to the time domain.
Probably the area in which physiological monitoring has reached its greatest degree of sophistication within the digital realm is in speech recognition. Though the speech to be processed may not be medical data in the truest sense of the word, yet using a very broad definition of physiological parameters, we can include speech. An example of a speech processing technique may be found in U.S. Pat. No. 4,227,177 issued to Moshier. Notice that the speech is input in an amplitude versus time domain signal and a corresponding truly digital signal is produced whose nature is that of text. The major difference, however, between this type of speech recognition and true monitoring for medical diagnostic purposes is that, though the speech is transformed into digital signals, the digital signals correspond only to what is said and not how it was said. That is to say, the effects of the time domain are totally excluded during the transformation process.
An interesting technique for attempting to recognize emotional state of a person from speech may be found in U.S. Pat. No. 4,093,821 issued to Williamson. Notice that in Williamson an attempt is made to analyze the signals within the time domain to determine the emotional state of the person applying the input. This technique being suitable to accomplish the purposes stated in the reference is probably not sufficiently accurate, nor precise enough, for medical purposes.
An example of a system which records information--in this case--in an analog format, and time tags that information to enable reconstruction of the time domain is found in U.S. Pat. No. 4,123,785 issued to Cherry, et al. This references teaches the use of a portable recorder for recording EKG information which also records a separate time mark to enable the monitoring and analysis apparatus to reconstruct that time domain for the purposes of providing its analysis and output. Notice, however, that the information that is recorded on the portable monitoring device is actually recorded as an analog signal.
The actual parameter chosen by the inventors to be monitored by the system disclosed herein is the audio click produced by the operation of a prosthetic heart valve. It has been shown in the art that such devices emit signals having specific frequency components. Subsequent embolotic buildup on these prosthetic heart valves tends to change the characteristic frequency components of the clicks. A first publication showing this effect is entitled "Sound Spectro Analytic Diagnosis of Malfunctioning Prosthetic Heart Valve" by Kagawa, et al in a paper originally delivered at the Sixtieth Anniversary of the First Department of Surgery, Tohoku University School of Medicine and subsequently published in Experimental Medicine, Vol. 123, pp. 77-89, 1977. Notice that, whereas Kagawa, et al provides some theoretical basis for the monitoring disclosed herein, they provide no practical apparatus for technique for performing this monitoring.
A second reference providing a theoretical basis for this type of monitoring is found in an article "Real Time Sound Spectro Analysis for Diagnosis of Malfunctioning Prosthetic Heart Valves," by Kagawa, et al published in the Journal of Thoracic Cardiovascular Surgery, Vol. 79, pp. 671-679, 1980. In this later article, apparatus is shown at FIG. 1 for processing of this click information. Notice, however, that the processing is accomplished essentially in real time and occurs primarily in the time domain in analog form. Again, this subsequent article provides theoretical basis for the type of monitoring disclosed herein, but does not show hardware for a practical accomplishment of these monitoring objectives.